1. Field of the Invention
This invention relates generally to the field of optical temperature-measuring devices, which comprise a mass of luminescent sensor material and optical means to lead excitation light from a source of such light to the mass and to lead luminescent light created in the mass by the excitation light back to a detector. A preferred optical means is at least one optical fiber. The invention is primarily concerned with the nature of the sensor material for such measuring devices.
Optical temperature-measuring devices are a preferred choice in several specific fields of application, for example, where temperature is to be sensed in an environment where there is a high risk of electrical disturbances, an explosion hazard, a high magnetic or electrical field strength or where some other considerations call for an optical fiber or the like as a signal transmission medium. The majority of known temperature sensors for fiber optical measuring devices are based on generating a temperature-related wavelength shift, which has an important practical advantage in permitting their use in situations where there are relatively high attenuations of the light passing through the fibers and the junctions formed thereby. The disadvantage of using such sensors, is that they are relatively complicated and that their construction is relatively expensive.
In this specification the term "light" should be taken to include electromagnetic radiation in the infrared and ultraviolet and not just wavelengths in the visible spectrum.
The present invention solves the above-mentioned problems by using a special class of materials as the sensor material in an optical temperature-measuring device.
2. Description of the Prior Art
In U.S. patent application Ser. No. 480,671, filed on Mar. 31, 1983, in the names of Brogardh, Hok and Ovren (assigned to the assignee of this application) and in Swedish Pat. No. 431,128 (see corresponding U.S. patent application Ser. No. 498,477, filed on May 26, 1983) (also owned by the same assignee) luminescent transducers are disclosed which are based on sensor materials having atomically localized luminescence centers included as a solid solution in a monocrystalline or amorphous carrier material. This class of sensor materials, as pointed out in the above-mentioned applications, give so-called optical time constants in the range of hundreds of micro-seconds. The measurement of a time constant of the order of hundreds of micro-seconds may be performed in a simple manner employing a single optical fiber, which is thereby utilized both for the transmission of pulses of excitation light to the transducer and for the feedback of the luminescence light from the sensor material. Since the signal content which is indicating the temperature being measured exists in the form of a time constant, the optical construction for the detector equipment is considerably simplified and can thus be less expensive than a detector based on measuring a wavelength displacement. The abovementioned patent applications describe transducers for measuring a number of physical quantities.